Curing olefin-diolefin copolymers



Patented. July 13, 1948 UNITED. STATES PATENT OFFICE Robert R. Sterrett,Nauzatuck, com,

United States Rubber Company,

assignor to New York,

N. Y., a corporation of New Jersey No Application January 15, 1944,

Serial No. 518,415

This invention relates to improvements in curing butyl rubber, which isconsidered to be a copolymer of a mono-olefine and a diolefine,forpresence of selected inorganic and/or organic oxidizing agents,vulcanize the synthetic rubber known as butyl rubber. The vulcanizationis quite rapid, and in many instances it results in scorched stockswhich causes waste and delay.

Scorch is defined as a premature partial vulcanization of the stockbrought about by heat present or developed during processing. A scorchedstock is no longer completely thermoplastic and cannot be smoothlysheeted or extruded. Scorch lif e, as determined by the Mooneyplastometer, is a measure of the time during which the stock may besafely processed. The exact time will depend largely on processingtemperature and to some extent on the processing operation being carriedout. A Mooney scorch resistance (defined below) of ten minutes at 250 F.is considered satisfactory for factory processing of Hevea rubber tread'stocks under ideal conditions. A longer time is desirable to provide afactor of safety.

I have found that by adding a thiuramdisulfide having the structure ll gin which the terminal nitrogen is bonded to aliphatic hydrocarbonradicals such of alkyl or cycloalkyl (e. g., ethyl, butyl, amyl,cycle-pentamethylene, benzyl, etc.) and particularly atetraalkylthiuramdisulfide, to a butyl rubber mix which is to be vulcanized with amember of the above referred to quinone dioximino class of nonsulfurvulcanizing agents, that the rate of cure can be greatly reduced andscorching prevented. Based on 100 parts, by weight, of the butyl rubberthe amount of the disulfide is proportioned, according to the amount ofthe said'vulcanizing agent used, to be in amount suflicient to properlyset the stock with substantially no scorching. Generally, the amountsused may range from ,01 to about 4 parts of the disulfide per 100 parts01' the rubber, although in certain cases more may be used.

The following examples, in which the parts are by weight, illustrate theinvention, it being understood that the invention is not to be limitedthereto:

- Example 1 g B Butyl rubber 100.0 100.0 Carbon black 60.0 60.0 Stearicacid 3.0 3.0 Sulfur A 1.5 1.5 Zinc oxide 5 .0 5.0 P1002 6.0 w 6.0Para-quinone dioxime 2.0 2.0 2.0

Tetromethyl thiuramdisulfideuu In milling the above mixes, A set up onthe mill, while B mixed normally. The temperature of the mix did notexceed 210 F.

Example 2 a Butyl rubber 100.0 100.0-

Carbon black 60.0 60.0

Stearic acid 3.0 3.0

Sulfur 1.5 1.5

Zinc oxide 5.0 5.0

Pba04 10.0 10.0

Para-quinone dioxime 2.0 2.0 0.5

Tetramethyl thiuramdisulfide Mooney Pla s-tometer Scorch Resistance at 1minute 4 minutes of increase of the Mooney two units per minute atstituted thluramdiaulndes such as dibenzyl tmummmmm 7 REFERENCES CITEDHaving thus described my invention. what I The following references areor record in the claim and desire to protect by Letters Patent is: fileof this patent: A method of reducing the rate of cure or a mb- 5 muTEDbery copolymer of a major proportion of a mono- STATES PATENTSlso-olefln and a minor proportion of a conjugated Number Name Datedlolefin vulcanized with an oxidizing agent and 1 .004 Thomas et al Feb.16, 1943 p-qulnone dloxime, which comprises additionally .7 Roberts Dec.25, 1945 adding to the stock before cure a small amount 01' 1otetramethyl thiuramdisulflde.

ROBER'I? R. STERRE'I'I'.

